1. Field of the Invention
The present invention relates to a printed circuit board on which various circuit elements are mounted and to a method of manufacturing such a printed circuit board.
2. Description of Related Art
In a process of manufacturing a conventional printed circuit board that includes a through-hole positioned near a circuit element, an opening area of the through-hole is covered with a masking tape or the like before dampproof liquid is coated on the circuit element in order to prevent the dampproof liquid from flowing into the through-hole. The process of covering the opening area of the through-hole is referred to as a masking process. Since some of the circuit elements have to be protected from moisture or water, the dampproof liquid is coated thereon after such circuit elements are mounted on a substrate. However, the dampproof liquid coated on the circuit elements flows into the through-hole formed near the circuit elements, contaminating the through-hole with the dampproof liquid, if the through-hole is not covered by the masking tape or the like.
A lead wire or a terminal pin is inserted into the through-hole having a metal-plated inner bore and soldered to the inner bore or electrically connected thereto without soldering. If the through-hole is contaminated with the dampproof liquid, the electrical connection in the through-hole may be damaged. To prevent the dampproof liquid from flowing into the through-hole, the area around the opening of the through-hole is covered with the masking tape or the like in the conventional process of manufacturing the printed circuit board. However, positioning the masking tape precisely in a required area is not easy because the circuit elements and the through-hole are usually positioned close to one another. Although the masking tape may be automatically placed by an automatic machine, it is difficult to eliminate small positioning errors in a range of 1 mm. It may be possible to exactly position the masking tape by using an expensive and sophisticated positioning machine. However, employing such a sophisticated machine in the masking process would not be justified from a view point of a manufacturing cost.